1. Field of the Invention
The present invention relates to ball screw modules, and more particularly, to a ball screw module having a circulating device mounted on a nut member thereof.
2. Description of the Prior Art
The operating principles of a conventional ball screw shaft involve providing balls between a screw shaft and a nut member so as to replace the sliding friction transmission of an outdated acme screw shaft (ACME) with ball rolling motion, thereby reducing friction-induced wear and tear greatly and maintaining high efficiency and high preciseness.
Balls are effective in enabling a screw shaft to move smoothly. However, adjacent balls are, in the course of rolling, likely to collide with each other and therefore produce much noise. The collision shortens the service life of the balls and therefore shortens the service life of the screw shaft.
To solve the problems, the prior art disclosed a connector whereby balls are fixed in position. U.S. Pat. No. 5,993,064 further provides an improved ball connector made of resilient material and comprising four belt members for fixing a plurality of balls in position in all directions, and a ball connector capable of bending freely in all directions and yet keeping the respective positions of the balls unchanged, such that the ball connector is applicable to linear sliding and ball screw shafts.
However, a ball screw module requires a circulating route for guiding the balls returning to a spiral-shaped groove so as to travel along a continuous ball track. A ball connector passing the circulating route has to change its direction of movement so as for the ball connector to follow a loop. An improperly designed circulating route is likely to prevent a ball connector from passing a circulating route smoothly and changing direction. Ball connectors disclosed in the prior art tend to sever when twisted and pulled unduly. Referring to FIG. 1, U.S. Pat. No. 5,993,064 taught a ball connector for use with a screw shaft, and taught a nut member having a circulating device disposed therein so as to enable the ball connector to go through a loop. U.S. Pat. No. 5,993,064 failed to teach how to enable the ball connector to pass the circulating device smoothly. In practice, the two lateral sides of a ball connector undergo 3D revolutions while traveling from a spiral track to a circulating device. If angles of a revolving route is not specially designed, a ball connector traveling along the revolving route is likely to have its inner side squeezed and its outer side pulled and therefore sever due to a difference between its inner and outer sides in deformation. Although linear rolling tracks using ball connectors are commercially available, ball screw shafts adopting ball connectors remain unavailable in terms of design and fabrication.